1. Field of the Invention
The present invention relates to an optical pickup and a disk drive device. Specifically, the present invention relates to a technical field of forming the boundary between the north and south poles of a tracking magnet by using an arbitrary line segment not being one straight line, to thereby suppress the generation of unnecessary torque in a tracking operation and a focusing operation and improve the transmission characteristic.
2. Description of the Related Art
There is a disk drive device which records and reproduces an information signal on and from a disk-like recording medium such as an optical disk and a magnetooptical disk. Such a disk drive device is provided with an optical pickup which is moved in the radial direction of the disk-like recording medium to apply laser light to the disk-like recording medium.
The optical pickup is provided with an objective lens drive device which includes a fixed block and a movable block supported by the fixed block via a plurality of supporting springs made of metal wire or the like (see Japanese Unexamined Patent Application Publication No. 2006-202380, for example).
In the optical pickup, the movable block including a lens holder for holding an objective lens is moved with respect to the fixed block in a focusing direction, which corresponds to a direction approaching or separating from a recording surface of the disk-like recording medium, to perform focus adjustment. Further, the movable block is moved with respect to the fixed block in a tracking direction, which substantially corresponds to the radial direction of the disk-like recording medium, to perform tracking adjustment. With the focus adjustment and the tracking adjustment described above, the spot of the laser light applied to the disk-like recording medium via the objective lens is collected on a recording track of the disk-like recording medium.
The objective lens drive device provided to the optical pickup is provided with a focusing magnetic circuit for moving the movable block in the focusing direction and a tracking magnetic circuit for moving the movable block in the tracking direction. The focusing magnetic circuit includes focusing coils and focusing magnets. The tracking magnetic circuit includes tracking coils and tracking magnets.
In the objective lens drive device, the movable block and the fixed block are connected to each other by the supporting springs, while being apart from each other in a tangential direction perpendicular to both the focusing direction and the tracking direction.
When the optical pickup is moved in the radial direction of the disk-like recording medium, the laser light is transmitted through an optical path opening formed in a surface of the lens holder opposite to a surface thereof facing the fixed block, and is incident on an upward reflecting mirror disposed below the objective lens. The laser light reflected by the upward reflecting mirror is applied to the recording surface of the disk-like recording medium via the objective lens. In this process, the focus adjustment and the tracking adjustment described above are performed such that the spot of the laser light applied to the disk-like recording medium via the objective lens is collected on the recording track of the disk-like recording medium.
The objective lens drive device includes an objective lens drive device in which symmetrical magnetic circuits are provided on both sides of the objective lens in the tangential direction. In this type of objective lens drive device, it is necessary to provide one of the magnetic circuits at a position shifted from the optical path opening. Therefore, the thickness (height) of the movable block is increased, and there arises an issue of difficulty in slimming down the objective lens drive device.
Meanwhile, the objective lens drive device includes another type of objective lens drive device in which the magnetic circuit is provided only on the fixed block side of the movable block. In this type of objective lens drive device, the upward reflecting mirror is disposed at a height substantially the same as the position (height) of the magnetic circuit provided on the fixed block side of the movable block. Therefore, the objective lens drive device is slimmed down.
However, the objective lens included in the movable block has a large weight. In the objective lens drive device provided with the magnetic circuit only on the fixed block side of the movable block, therefore, it is necessary to provide a balancer on the opposite side of the objective lens across the magnetic circuit to set the centroid of the movable block in the vicinity of the magnetic circuit. In this type of objective lens drive device provided with the magnetic circuit only on the fixed block side of the movable block, therefore, the provided balancer increases the weight of the movable block, and causes a decrease in sensitivity in the movement of the movable block.
Further, in this type of objective lens drive device provided with the magnetic circuit only on the fixed block side of the movable block, the objective lens, the magnetic circuit, and the balancer are sequentially provided in the tangential direction. Therefore, the length in the tangential direction of the movable block is increased, and the high-order resonance characteristic is deteriorated.
In view of the above, there is an objective lens drive device in which the centroid of the movable block is positioned to be closer to the objective lens than to the magnetic circuit to improve the sensitivity and the high-order resonance characteristic while slimming down the objective lens drive device (see FIG. 13).